Conventional dynamoelectric machines, such as generators used with gas and steam turbine drives employ forged rotors of magnetic material into which slots are machined for receiving the conductive turns of field windings which are interconnected so as to produce a desired magnetic flux pattern. The rotor may be pedestal mounted so as to be rotated on an axis to cause the flux pattern to interact with stator windings such that electric power is generated in response to the rotation supplied by a turbine or other motive device or a rotational torque is generated responsive to input electrical energy.
FIG. 1 is illustrative of a conventional generator rotor 1 constructed of a single-piece forging having coil slots 2, winding retainer rings 3, a fan 4 for stator winding ventilation, as well as shaft bearing surfaces and couplings.
The rotor windings are conventionally directly cooled by way of a radial flow design of coolant gases through openings in the winding conductors and insulating layers. Such coolant gas is supplied via subslots in the rotor winding slots wherein the coolant gases move axially through the subslots and radially through the winding flow channels. The manner in which the rotor slots are shaped and insulated, as well as the efficiency of the flow channels for eliminating heat from the windings present formidable space utilization design problems, particularly where high maximum permissible current limits are contemplated. Additionally, design considerations involve obtaining sufficient clearance for ventilation passages along with relatively high winding slot fill factors as well as insulating the individual winding turns from each other and from the rotor forging.
In this regard, FIG. 2 illustrates the present conventional practice of including one coil per slot wherein the coil turn conductors 20 are nearly the full width of the slot with only sufficient coil installation clearance between conductors and the forging to allow the inclusion of slot armor 21 to be used for insulating the turns from the rotor: forging. Additionally, turn insulation 22 in the form of insulating strips are used between each turn conductor for insulating the individual winding turns from each other.
Such conventional slot configurations, as illustrated in U.S. Pat. No. 4,859,891 issued to Jenkins et al on Aug. 22, 1989, may include a U-shaped subslot liner for supporting the coil turn conductor 20, which in combination with a single U-shaped slot armor or two L-shaped portions of slot armor serve to support and insulate the turns from the metal rotor forging. Additionally included in such conventional rotor slots are creepage blocks 26 at both the top and bottom ends of the slot (only one of which is illustrated in FIG. 2), as well as dovetail wedges 24 for resisting the radially outward forces exerted on the windings when the rotor is operational. Further illustrated elements include radially directed passages 25 which are punched or machined slots in each of the winding turns, as well as the turn insulation, for providing radial ventilation passages. The U-shaped subslot liner 23 and the lower winding turn or creepage block provide an axial channel or subslot for furnishing a supply of coolant gas, such as air, to each of the ventilating passages or slots in the winding turns and turn insulation so as to provide high velocity gas, thus cooling the copper winding turns.
Still other slot configurations with relatively narrow machined subslots using subslot covers for supporting the winding turns are known, as may be seen from the disclosure in the aforementioned Jenkins et al patent. Still another approach may be seen from a review of U.S. Pat. No. 5,065,064 issued to Kaminski on Nov. 12, 1991, wherein the rotor slot insulation includes two insulating slot armors, each of which extends in an offset manner through the transition between the rotor slot and subslot, thus eliminating the need for a subslot cover.
In each of the above referenced configurations the slots, subslots, windings and insulation extend the full length of the rotor. Coolant gas enters through the full length subslots and is discharged into the air gap between rotor and stator along the length of the rotor body through radial slots that are machined or punched in the copper coil turn conductors, turn insulation, creepage blocks and wedges. As aforementioned, present design practice involves the use of one coil per rotor slot wherein the copper coil turn conductors are nearly the full width of the slot. As illustrated in FIG. 3, such full width slot coil turn conductors 30 separated by turn insulation strips 31 are formed into coils by brazing straight rectangular copper sections to them at their ends. The thus formed coils are inserted into a slot 32 after brazing and cleaning. Aligned ventilating slots such as 33, for example, may be included in both the copper coil turn conductors and insulating turn separators to allow the radial flow of coolant gases. Additionally, lateral grooves 34 may be included in the end turns to allow the circumferential flow of coolant gases.
I have discovered that the use of two coils per slot wherein the central coil sides are separated by insulating spacers driven between the coils after they are wound offers several advantages in the construction, operation and repair of such dynamoelectric machines. That is to say, the separation of the coils by a plurality of spacers distributed in a spaced relationship along the axial length of the rotor slots not only serves to electrically insulate the coils from each other but additionally form ventilating passages between the coil sides and spacers for allowing the radial flow of coolant gases. Additionally, the spacing between the two coils allows the coils to be forced away from the slot armor, thus allowing the replacement of damaged slot armor insulation. Moreover, after the insulating spacers are driven in place, no clearance exists between the rotor slot sidewalls, the slot armor and the coil sides, thus heat transfer from the copper coil turns to the steel rotor forging will increase resulting in lower copper temperatures. A further advantage of the disclosed structure is that the reduction in slot side clearance allows increased ventilation passage size or results in a better slot fill factor.
Still further advantages may be realized by my winding design. For example, since the coil turns are approximately half the normal width, they may be wound in place from a long length of conductor. Such winding would have the advantage of eliminating the brazing and cleaning of the aforementioned fabricated rotor windings even in the event that the increased stresses produced by winding the coils in place resulted in damaged slot armor. As aforementioned, the slot armor could be easily replaced without removing the coil from the slot. Moreover, although in some known indirectly cooled single full width coil rotor designs the coil end turns are formed by bending rather than the aforementioned brazing, relatively large upsets occur at the corners due to the bending of the rather wide full width coil turn conductors. Such upsets or dimensional irregularities in turn require pressing and/or grinding to eliminate the upsets. In contrast, where two coils are wound in the same slot bending of the relatively narrow coil conductors results in much less upset or dimensional irregularities in the half width conductors. Thus, only pressing may be required.
Additionally, it will be noted from the detailed description of the invention which follows, that the ability to install slot armor in the slot sides adjacent to the rotor poles after the coils are in place allows the distance between the ends of the rotor forging and the nearest end turn winding to be reduced. Thus, a reduction in effective rotor length or a relative increase in active machine length may be obtained.
These and further objectives and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.